The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 199 03 943.7, filed on Jan. 28, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a process for producing a fibrous material web, e.g., a paper or cardboard web, from a fibrous material suspension. The invention also relates to a device for carrying out the process.
2. Discussion of Background Information
A starting point for the instant invention is European Patent Application EP 0 894 894, which was not published prior to the above-noted priority date of the instant application. EP 0 894 894, which is expressly incorporated by reference herein in its entirety, discloses the formation of a fibrous material web between two endless, water-permeable belts, preferably wire belts, which occurs in a known manner by virtue of the fact that a portion of the suspension fluid is removed through the belts. In a part of the web-forming zone, the belts, together with the fibrous material web being forming between them, is guided between so-called uniform pressure drainage elements, in the form of, e.g., perforated plates. A disclosed embodiment provides for an additive, e.g., ink, filler, adhesive, draining agent, to be supplied to the fibrous material web being formed by flowing through one of the uniform pressure drainage elements and through the porous belt traveling atop the forming web.
The present invention improves the web forming process and the apparatus for performing the process to the extent that certain properties of the finished fibrous material web are improved.
As a result, a number of requirements should be fulfilled, if possible. For example, the so-called xe2x80x9ctwo-sidednessxe2x80x9d of the fibrous material web can be deliberately influenced, i.e., to achieve as little two-sidedness as possible so that substantially uniform properties occur on both sides of the web or to produce an xe2x80x9cintentional two-sidednessxe2x80x9d so that the two sides of the fibrous material web have different properties.
An additive can be supplied to the fibrous material web, and a rinsing-out of the additive should be prevented to the greatest extent possible during subsequent draining of the fibrous material web.
When producing multi-ply products, the fibrous material web produced to be united with another fibrous material web should include a ply bond between the two webs that is as high as possible.
The cross profile of particular web properties should be influenced and/or adjusted.
The intensity of drainage in particular partial regions of the web-forming zone can be influenced and/or adjusted.
Accordingly, the process in accordance with the instant invention provides that the supply of the additive is controlled or regulated such that the fibrous material web formed has the respectively deliberate (i.e., either slight or clearly perceptible) two-sidedness. In other words, the supply of the additive is controlled or regulated so that, with regard to a particular surface quality (or with regard to a particular quality level that can be measured on the surfaces of the web), a particular ratio is produced between the properties or quality levels of the two sides of the web.
In an exemplary embodiment of the process according to the invention, during a continuous manufacturing process, a particular property can be continuously measured on both sides of the traveling fibrous material web (e.g., paper web). Thus, a continuous determination may be made as to whether the intended degree of two-sidedness is being achieved.
If the degree of two-sidedness deviates from an intended value of two-sidedness (i.e., a set point), then a volume flow and/or a pressure of the additive being supplied, for example, can be varied so that the two-sidedness of the material web being formed approaches the set point, e.g., with the aid of a closed control loop. By varying the pressure, the penetration depth of the additive, among other things, can be deliberately controlled, which can lead to an optimization of the distribution of additive in the Z-direction.
A particularly important further concept of the invention is that a fine fibrous material suspension can be used as an additive. The fine fibrous material suspension can be obtained, e.g., from suspension fluid removed in a beginning region of a twin wire zone, i.e., the so-called xe2x80x9cwhite water.xe2x80x9d In this instance, a definite, e.g., particularly high, fines content can be produced on one of the two sides of the fibrous material web or on both sides of the web. The level of the fines content is important, for example, for the printability of the finished fibrous material web. In a similar manner, it is important in the production of a multi-ply product that, before the two fibrous material webs are united, the fines content on the web sides to be joined together, or arranged to come into contact with one another, can be increased to the greatest extent possible. Other possible additives include, e.g., filler suspension, polymer solution, adhesive solution, or starch solution, or an ink that is supplied, for example, at a particular location.
When utilizing the process according to the invention, the location of the additive supply is in a vicinity of the so-called xe2x80x9cuniform pressure drainage.xe2x80x9d This is the region of web formation in which drainage occurs through the use of an essentially pulsation-free drainage pressure. In this regard, in a relevant part of the web-forming zone, drainage pressure either remains essentially the same or changes almost continuously, e.g., increases. Consequently, drainage of this type differs from the drainage method normally used in the beginning region of the web formation in which, with the aid of so-called xe2x80x9cforming strips,xe2x80x9d pressure pulsations are produced in the suspension while it is present between the belts. This results in the fibrous material remaining as uniformly distributed as possible during the web formation process.
A particular advantage of the supply location (for the additive) in the vicinity of the uniform pressure drainage is that, after the supply of the additive, the subsequent drainage can be controlled so that as little as possible of the supplied additive is lost. This is achieved, e.g., by virtue of the fact that the additive is supplied at the beginning region or in the middle region of the uniform pressure drainage zone and that, downstream of the supply point, the intensity of the subsequent drainage can be reduced on the relevant side of the web, and may even be, e.g., completely suppressed in a particular section. At the same time, the intensity of drainage on the opposite web side can be increased through the use of, e.g., a vacuum and by providing increased perforation cross-sections in a particular region.
The prevention of drainage on the side of the web on which the additive has been supplied is possible, e.g., by virtue of the fact that either a closed, i.e., non-perforated, plate element is provided in a particular partial region of the uniform pressure drainage zone or a part of the perforation is closed, e.g., with the aid of a compressed air buffer. In any case, it can be assured that a very high retention of the supplied additives can be expected. Otherwise, the invention also assures that the fines and/or fillers contained in the fibrous material suspension from the beginning are retained to a higher percentage than previously in the fibrous material web being formed.
In an alternative embodiment, and with the aid of uniform pressure drainage elements of different permeabilities, it is possible to assure that drainage through one belt is more intense than the drainage through the other belt. In extreme cases, in a particular region of the uniform pressure drainage zone, the removal of suspension fluid through one of the two belts can be suppressed at least to a large extent, e.g., with the aid of a water-impermeable uniform pressure drainage element. The latter assures that, on this side of the fibrous material web being formed, the fines and/or fillers that are supplied with the fibrous material suspension cannot escape. As a result, a fibrous material web is obtained which has a considerably higher proportion of fines and/or fillers on one side of the web.
The present invention also includes possibly advantageous measures for the additional control of the drainage intensity and for the most uniform possible distribution of the fibrous material, which can be utilized in combination or independently of the other features of the invention.
Numerous other possibilities for embodying the process according to the invention and the device according to the invention are contained in the Patent Application EP 0 894 894 mentioned at the beginning. Further, it is expressly emphasized that all features described in the European application, which was unpublished at the time of the filing of the priority application, can be combined with the features of the current application. Accordingly, the disclosure of EP 0 894 894 is expressly incorporated by reference herein in its entirety.
The present invention is directed to a process for producing a fibrous material web from a fibrous material suspension. The process includes conveying the fibrous material suspension between two endless, continuously revolving porous belts positioned to form a twin wire zone, removing a part of the suspension fluid through the porous belts so that the fibrous material web begins forming between the belts, guiding the two endless belts and the material web being formed therebetween through uniform pressure drainage elements, and removing additional suspension fluid with the uniform pressure drainage elements. The process further includes supplying an additive though at least one of the belts to the forming fibrous material web in a vicinity of the uniform pressure drainage, and one of controlling and regulating the supply of the additive to provide a particular ratio between quality levels of a top side of the forming web and a web underside of the forming web.
According to a feature of the present invention, the supply of the additive can be one of controlled and regulated so that the quality levels for each side of the forming web are substantially the same.
In accordance with another feature of the invention, the supply of the additive can be one of controlled and regulated so that the quality levels for each side of the forming web are unequal.
In accordance with a further feature of the present invention, the supply of the additive to be one of controlled and regulated can be a volume flow.
According to a still further feature of the invention, a pressure of the supply of the additive may be one of controlled and regulated. The pressure of the additive can be one of controlled and regulated through the admixture of a propellant. The propellant can include at least one of compressed air and steam.
The additive may be supplied in one of a beginning region and a middle region of the uniform pressure drainage elements. An intensity of drainage can be reduced on a side of the web on which the additive is supplied at a location downstream from where the additive is supplied.
Further, the additive can include a fine fibrous material. The fine fibrous material may include the suspension fluid removed in a beginning region of the twin wire zone. While the fibrous material web is still moist, and the process can further include uniting the still moist fibrous material web with another fibrous material web, thereby producing a multi-ply fibrous material web. Sides of the still moist web and of the another fibrous web having an increased fines content are brought together in uniting the still moist fibrous material web with the another fibrous material web.
In accordance with another feature of the instant invention, the additive can be sectionally supplied to the region of the uniform pressure drainage elements by a plurality of individually controllable section lines distributed across a width of the web.
Further, the fibrous material web can include one of a paper and a cardboard web. The quality level may be related to fines content, and the revolving porous belt can include wire belts.
The present invention is directed to a process for producing a fibrous material web from a fibrous material suspension. The process includes conveying the fibrous material suspension between two endless, continuously revolving porous belts positioned to form a twin wire zone, removing a part of the suspension fluid through the porous belts so that the fibrous material web begins forming between the belts, guiding the two endless belts and the material web forming therebetween through uniform pressure drainage elements, and removing additional suspension fluid with the uniform pressure drainage elements so that, in a vicinity of the uniform pressure drainage elements, drainage occurs through the one of the two belts more intensely than through the other belt. In this manner, different quality levels are produced on the sides of the fibrous material web being formed.
In at least one partial region of the uniform pressure drainage elements, the process may further include suppressing removal of suspension fluid through one of the two belts. Further, the removal of the suspension fluid may be suppressed via a water-impermeable uniform pressure drainage elements.
According to a feature of the instant invention, the uniform pressure drainage elements located on opposite sides of the fibrous material web being formed may have different permeabilities.
The present invention is directed to an apparatus for producing a fibrous material web from a fibrous material suspension. The apparatus includes two endless, continuously revolving belts positioned to form a twin wire zone. The twin wire zone includes an inlet adapted to receive a suspension flow and the belts are porous so as to enable flow of suspension fluid therethrough. Uniform pressure drainage elements are positioned such that the belts, with the fibrous material therebetween, are guided through, and in contact with, the uniform pressure drainage elements. The uniform pressure drainage elements include a portion supporting the belts having at least one of a perforated and recessed surface adapted for receiving suspension fluid, so that drainage occurs through an essentially pulsation-free drainage pressure. A supply device for an additive can be coupled to at least one of the uniform pressure drainage elements, and a control or regulation device is provided to vary at least one of a volume flow and a pressure of the additive to be supplied.
The supply device can be coupled to a propellant supply device. The propellant supply can include at least one of compressed air and steam.
Further, the supply device may be coupled to one of a beginning region and a middle region of the uniform pressure drainage elements. At least one uniform pressure drainage element can be positioned downstream, relative to a belt travel direction, from the supply device coupling, and the at least one uniform pressure drainage element may be adapted to reduce drainage intensity relative to others of the uniform pressure drainage elements. The at least one uniform pressure drainage element can include a non-perforated plate.
According to a feature of the invention, the supply device can include a plurality of sections arranged across a with of the web, and an individually controllable section line feeds into each of the plurality of sections, thereby supplying a partial quantity of the additive.
In accordance with another feature of the invention, at least one of the uniform pressure drainage elements can be associated with a movable cleaning device.
Moreover, a distance between successively arranged uniform pressure drainage elements in a belt travel direction can be variable. At least one of the successively arranged uniform pressure drainage elements can be shiftable relative to the other, and the distance can be between approximately 0 and 50 mm.
In accordance with a further feature of the present invention, the uniform pressure drainage elements can include a plate-shaped perforated drainage element positioned against one of the two belts, and a plurality of forming strips positioned against the other of the two belts and opposite the plate-shaped element. Widths of the forming strips, relative to a web travel direction, may differ from one another. Further, distances between the forming strips may differ from one another. Still further, one of the plate-shaped drainage element and the forming strips can be flexibly pressed against the relevant belt.
The present invention is directed to an apparatus for producing a fibrous material web from a fibrous material suspension. The apparatus includes two endless, continuously revolving belts positioned to form a twin wire zone, where the twin wire zone includes an inlet adapted to receive a suspension flow and the belts being porous so as to enable flow of suspension fluid therethrough. Uniform pressure drainage elements are positioned such that the belts, with the fibrous material therebetween, are guided through, and in contact with, the uniform pressure drainage elements. The uniform pressure drainage elements located on one side of the belts enable greater drainage than through the uniform pressure drainage elements on the other side of the belts.
According to yet another feature of the instant invention, the uniform pressure drainage elements on the other side of the belt can include non-porous pressing surfaces.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.